1. Field of the Invention
The present invention relates to an electrostatic chuck and a manufacturing method for the same, and an alumina sintered member and a manufacturing method for the same.
2. Description of the Related Art
An electrostatic chuck is utilized to hold a glass substrate or silicon wafer during a semiconductor manufacturing process or a liquid crystal display manufacturing process. The electrostatic chuck holds a substrate using the electrostatic force and generally has a structure with a dielectric layer stacked on an electrode. After a substrate is mounted on a dielectric layer, the electrostatic chuck holds the substrate on the dielectric layer using the electrostatic force called Coulomb force, which is generated between the substrate and the electrode. Alternatively, the electrostatic chuck holds a substrate on a dielectric layer using the electrostatic force called Johnsen-Rahbek force (hereafter, called ‘J-R force’), which is generated between the substrate and the surface of the dielectric layer.
The electrostatic chuck using Coulomb force (hereafter, called a Coulomb-type electrostatic chuck) uses as a dielectric layer a highly insulating material having a volume resistivity equal to or greater than 14Ω·cm in an operating temperature. The electrostatic chuck using the J-R force (hereafter, called a J-R type electrostatic chuck) uses as a dielectric layer a material having a volume resistivity equal to or less than 1014Ω·cm in an operating temperature.
Resin such as polyimide resin, and a ceramic material such as aluminum nitride (AlN) or alumina (Al2O3) are well known to be used as a material for the dielectric layer. The electrostatic chuck using resin such as polyimide resin is inexpensive, however, the corrosion resistance and heat-resistance thereof are limited. For example, in a high temperature range of 100° C. or greater, usage thereof is difficult. On the other hand, the electrostatic chuck using a ceramic material such as aluminum nitride or alumina has better characteristics in corrosion resistance and heat-resistance.
Precisely, the aluminum nitride cannot have very high volume resistivity, which limits allowable operating temperature range when using that aluminum nitride as the Coulomb-type electrostatic chuck. Therefore, that aluminum nitride is often used for the J-R type electrostatic chuck.
A dielectric alumina layer formed by spraying so as to decrease the process cost is well known. Alumina provided by plasma-spraying has a volume resistivity equal to or less than 14Ω·cm at a temperature of 20° C., for example, which is not very high in resistance. To solve this problem, an electrostatic chuck with an adjusted volume resistivity ranging between 109 and 1011Ω·cm at a temperature of 100° C. or less, which is provided by adding an additive such as TiO2 to alumina, has been proposed (see Japanese Patent Application Laid-open Hei 3-204924.) Moreover, an electrostatic chuck with volume resistivity ranging between 108 and 1015Ω·cm at room temperature, which is provided by adding SiC to alumina so as to improve corrosion resistance and strength, has been proposed (see Japanese Patent 3348140.)
Furthermore, an electrostatic chuck using sintered alumina with an adjusted volume resistivity ranging between 1014 and 1016Ω·cm at a temperature of 200° C. or less has been proposed (see Japanese Patent Application Laid-open 2003-152065.) As disclosed therein, the conventional electrostatic chuck using alumina as a dielectric layer uses an additive added dielectric alumina layer, in order to reduce a volume resistivity and enhance strength and corrosion resistance. Even with the electrostatic chuck using comparatively high volume resistivity, the volume resistivity of the dielectric alumina layer is 1016Ω·cm or less.
However, an aluminum nitride has comparatively high volume resistivity and semiconductor characteristics. Therefore, the electrostatic chuck using an aluminum nitride of the ceramic materials as a dielectric layer cannot maintain a high chucking force in the range from a low to a high temperature, since the resistance strongly depends on temperature. In addition, it is difficult to control leakage current.
Thus, the J-R type electrostatic chuck using an aluminum nitride with comparatively low resistance as a dielectric layer cannot avoid leakage current. On the other hand, the Coulomb-type electrostatic chuck has little leakage current, however, residual charge tends to remain on the surface of the electrostatic chuck. This leads to a problem of poor substrate dechucking response when the volume resistivity of the dielectric layer is not high.
Moreover, a conventional electrostatic chuck using alumina with comparatively high resistance added an additive causes wafer contamination and leakage current. Also, with the electrostatic chuck using alumina with comparatively high resistance as a dielectric layer, the volume resistivity reduces as temperature rises. Consequently, the substrate dechucking response gets worse. In other words, the conventional chuck can be used only within a narrow temperature range. Moreover, an alumina member is not provided to maintain excellent electrical insulation over a wide temperature range.